1. Field of the Invention
The present invention, in general, relates to a powertrain for a hybrid vehicle, and, more particularly, to a powertrain for a hybrid vehicle which is advantageous in terms of improvement of fuel efficiency, weight, and manufacturing cost without a requiring a valve body and an oil pump for hydraulic pressure by replacing a brake with a dog clutch, because, in the related art, when a vehicle runs in a high-speed period, a brake is connected to a motor generator and a so-called overdrive (OD) gear ratio is implemented, but according to the configuration of the present invention, there is no need for a valve body and an oil pump for hydraulic pressure for operating the brake.
2. Description of Related Art
A hybrid vehicle equipped with a hybrid transmission composed of an engine, a motor generator, and a planetary gear set can run in an electric vehicle mode for driving the vehicle only with the motor usually during starting and in a low-speed period, and when the vehicle speed increases, the transmission operates as an EVT (Electrically Variable Transmission), so the vehicle can run in a power division mode for more efficient use of the engine power and the motor power, in which, similar to the existing transmission, a fixed gear ratio can be used to further improve power performance of the vehicle.
A system based on this concept is designed to improve an idle-stop function, maximize regenerative braking, and improve fuel efficiency and power performance of a vehicle.
Further, no exhaust gas is produced by the engine and the engine can be driven with optimum fuel efficiency while the hybrid vehicle is driven by only the motor generator, so it is recognized as an environment-friendly automotive technology having the advantage of improved fuel efficiency and reduced exhaust gas.
The power transmission system of such a hybrid vehicle may be designed to implement various driving modes with a simple configuration in order to improve fuel efficiency of the vehicle and to improve drivability of the vehicle, for example, improving acceleration ability, by changing the driving modes in accordance with the driving conditions of the vehicle.
FIG. 1 shows a layout of a transmission of a hybrid vehicle in the related art and FIG. 2A and FIG. 2B are views showing shifting for overdriving in a high-speed period. Problems in overdriving due to the layout of a transmission in the related art are described hereafter with reference to the accompanying drawings.
The thick lines in the layout of a transmission shown in the drawings indicate power transmission paths.
As shown in the figures, a brake 30 is coupled to an input shaft 20 connected to a motor generator 10.
Before the brake 30 is coupled to the input shaft 20, a process of stopping revolution of the motor generator by means of an external power supply was performed to overdrive a vehicle, but efficiency of the vehicle and fuel efficiency are decreased due to the continuous power supply, so the layout that restricts the motor generator 10 with the brake 10, as in FIG. 1, has been proposed.
Shifting by the layout of a transmission of the related art when a vehicle runs in a high-speed period is described hereafter with reference to FIG. 2A and FIG. 2B.
As shown in FIG. 2A and FIG. 2B, when a vehicle normally runs, shifting is performed by controlling a motor generator, and as the vehicle speed increases, hydraulic pressure is applied to a brake to implement an OD gear ratio, and the motor generator is restricted and a sun gear, that is one of the components of a planetary gear set 40 at a side of an engine, is restricted by the operation of the brake, thereby overdriving the vehicle.
That is, when a vehicle runs at an overdrive gear ratio in a high-speed period, the brake is connected to the motor generator and hydraulic pressure is applied to the brake, so the vehicle runs with the motor generator controlled; however, it is the problem of the related art that since the motor generator is controlled by the brake, there is a need for an oil pump for hydraulic pressure other than a valve body, so the fuel efficiency decreases and the weight and manufacturing cost increase.
Further, the brake itself acts as a ‘drag’ element in shifting while the vehicle runs.
Accordingly, the present invention provides a power train for a hybrid vehicle without a separate friction element such as a brake by replacing a brake controlling a motor generator with a dog clutch in order to achieve the function of synchronizing rotation speeds through revolution of a motor generator of the related art and to achieve the engagement function with the dog clutch.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.